1. Field of the Invention
The present invention relates to a manufacturing method of a light-focusing polymer GRIN(gradient index) lens which is used for focusing light in connections in the optical communications field, such as between optical fibers and between an optical fiber and an optical source. More particularly, the present invention relates to a manufacturing method of a polymer GRIN lens using the characteristics that the refractive-index of a directional polymer material is decreased by sulfonation.
2. Description of the Related Art
Recently, according to developments in the optical communication technology, many kinds of light-focusing lens have been developed for manufacturing integrated optical components.
Specially, GRIN lens manufactured medium having a refractive-index that sequentially changes according to the position can sharply decrease an aberration through the refractive-index distribution control. It has merits in that alignment is easy and an optical loss from an error of the alignment is decreased by utilizing a shape that is not a parabola, but a plane or a sphere.
In manufacturing these GRIN lenses, a glass or a polymer, etc, is largely used as the medium.
In the case of glass, it is manufactured by an ion-exchange method. On the other hand, in the case of a polymer, it is manufactured by a copolymerization method.
In the case of the ion-exchange method, it is easy to estimate the refractive-index distribution because the refractive-index distribution is formed by the diffusion of an ion. On the other hand, it takes a long time in the processing because the diffusion speed of an ion inside of glass is slow. Also it has a problem in that the ion-exchange temperature is limited by the softening temperature of the glass, but the ion-exchange is achieved at a higher temperature in the range of about 300-700 degrees.
On the other hand, the manufacturing method of a polymer GRIN lens using the copolymerization method has merit in that a variety of materials and various types of refractive-index distribution, depending on the materials can be obtained by obtaining a refractive-index distribution by copolymerizing at a temperature below 100 degree two or more monomers having a different response speed and a different refractive-index.
However, according to the copolymerization method, in the copolymerization due to the temperature or ultraviolet rays, the difference between the maximum refractive-index and the minimum refractive-index values is reduced. This is the result because the diffusion of monomers having a lower refractive-index is simultaneously performed, and also, because there are many variables that have an effect due to the kind of monomer, and a relative mixture ratio of monomer, a density and temperature, etc of a polymerization initiator. However, it is difficult to quantify the variables that have an effect on the refractive-index distribution. Consequently, it is difficult to control a process to obtain an optimum refractive-index distribution.